1. Field of Invention
The present invention relates in general to the field of fire extinguishment, prevention and suppression.
2. Background of the Invention
There are many fire extinguishing agents and methods for using the same. Some fire extinguishing agents operate by inerting or diluting mechanisms that deprive the fire of necessary chemicals, such as oxygen or fuels. Other agents chemically extinguish the fire, some by scavenging free radicals, thereby breaking the reaction chain required for combustion. Still others operate thermally to cool the fire.
Foams used for fire suppression include synthetic foams, aqueous film forming foams (AFFF), fluoroprotein foam, film forming fluoroprotein foam, and protein foams. There are many variations of components within each group. Some foams include an alcohol-resistant concentrate (ARC) such as a polymer that forms a protective layer between the burning surface and the foam which prevents foam breakdown by alcohols in burning fuel.
One of the most effective fire extinguishing agents, particularly for extinguishing flammable liquid fires such as fuel fires, is aqueous film forming foam (AFFF). This is a concentrated liquid which is diluted with water and applied to various classes of fires as a fire extinguishing agent. Upon application of the AFFF, the mixture becomes a foam and spreads over and floats on the surface of burning liquid. The agent contains a surfactant which reduces the surface tension of aqueous solutions to such a degree that the solution spreads upon a surface, such as gasoline, forming a vapor-sealing film which extinguishes the fire. The film also secures non-ignited areas and prevents ignition in those areas.
However, the prior art requires various components that are harmful to the environment, pose health threats, or allow flash and reignition.
Fire extinguishing agents formerly contained components (i.e. bromine-containing compounds such as Halon 1301) that were effective in fire fighting but were harmful to the ozone layer. Recognizing the dangers posed by the use of halons, the world community, through the Montreal Protocol, agreed to phase out halons. As a result, alternatives were developed that included fluorochemicals and inert gases.
However, the fire fighting foams containing fluorocarbons or other fluorochemicals are relatively inefficient. For example, U.S. Pat. Nos. 4,042,522 and 4,090,967 to Falk, U.S. Pat. No. 5,616,273 to Clark et al., U.S. Pat. No. 6,478,979 to Rivers, et al., U.S. Pat. No. 6,849,194 to Robin et al., U.S. Pat. No. 7,011,763 to Clark, and U.S. Pat. Nos. 7,216,722 and 7,223,351 to Sharma et al. describe AFFFs or agents of fire extinguishing compositions that contain fluorochemicals. Fluorocarbons can react in the flame to form decomposition products that pose a significant health threat. Fluorochemical surfactants have come under the scrutiny by the Environmental Protection Agency (EPA) and environmental organizations. For example, the EPA determined that perfluorooctanesulfonate posed a long-term threat to the environment after long-term studies of the agent were animal tested. The EPA has initiated other programs designed to evaluate potential environmental problems from other fluorochemical surfactants in the marketplace.
Another disadvantage of using fluorocarbons in fire extinguishing agents is that these chemicals react in the flame to form decomposition products that are corrosive to equipment and pose further health threats. It is desirable to preserve any equipment or machines on fire to the extent possible and to minimize any health threats from the fire fighting agent. Moreover, a less corrosive agent can be used in light weight containers made from substances such as aluminum instead of heavy, non-corrosive alloys.
Still other fire extinguishing agents contain inert gases such as nitrogen or argon and blends thereof which require large amounts of such gases to put out a fire because the agents are very inefficient at fire extinguishing. This creates a need for a large number of storage cylinders to store the agent and large storage spaces to house the cylinders. Furthermore, these agents are dangerous to people in proximity to the fire as the agents take away the oxygen in a confined space.
The prior art teaches fire fighting agents to blanket the surface of the flame and cut off oxygen to the flame. For example, see U.S. Pat. No. to Berger and U.S. Pat. No. 6,478,979 to Rivers. If the surface of the fire extinguishing product is broken, the fire will flash and reignite. This is true with both AFFF and ARC products.
As a result of the disadvantages of using the prior art in fire fighting, it is desirable to have fire extinguishing products that contain only a trace amount of fluorochemicals are not detrimental to human health or the environment, are inexpensive, and are easy to store. Moreover, it is desirable that improved fire extinguishing agents be developed that minimize re-ignition of the fire after application of the fire extinguishing agent.